BETTER PLANTS AND ANIMALS II 



saved and sown in a special plot, and in two years sufficient seed 

 had been obtained to warrant his putting it upon the market as 

 a new variety. This wheat, by virtue of its superiority, soon 

 came into general cultivation in Scotland, and spread into Eng- 

 land and France. Mr. Shirreff continued to select heads from 

 the better-appearing wheat plants in the fields of his neighbor- 

 hood and soon had as many as seventy different heads. He 

 planted the grains of each head separately, by what we now call 

 the ear-row method. He was thus able to compare the yields 

 and the characteristics of the plants of the different rows with 

 one another. Out of the seventy ear-rows, only three were 

 saved. These three strains, or, as we might say, varieties, 

 became quite generally distributed in Scotland and England, 

 and even spread to the Continent. 



These examples illustrate ways in which new varieties may 

 come into existence. We have obtained most of our improved 

 forms of plants through selection, which merely discovers and 

 preserves to our uses that which nature has in some unknown 

 way produced already. 



13. Variation in plants and animals. Everywhere in nature 

 there is variation, and variations give us the material from which to 

 make selection. No two plants or animals are ever exactly alike. 

 Sometimes, as in the case of the amount of sugar contained in 

 the sugar beet, it seems impossible to fix these variations by selec- 

 tion. In such a case we call them fluctuating variations, without 

 in any way understanding why they fluctuate. In other instances, 

 as in the case of corn with different numbers of kernel rows on 

 the ear, or of corn that bears its ears at different heights on the 

 stalk, it is possible to separate different breeds which will come 

 approximately true. An interesting experiment l with corn was 

 made which resulted in fixing the ears high or low on the stalk 

 by continued selection (Fig. 8). After six years of continued 

 selection there had been developed two kinds of corn one 

 bearing its ears at an average of four feet nine inches above the 

 ground, and another bearing its ears at an average of only two 



1 Bulletin 128, Illinois Experiment Station. 



